The present invention relates to a compact image recorder for recording a color image on a color photosensitive material at high speed.
Heretofore, a drum recording system has generally been used to record color images on a color photosensitive material by photo-exposing with electroimage signals. In this recording system, a photosensitive material cut to a desired size is wound on a drum and the drum turned to thereby modulate point sources scanned parallel to the drum axis.
However, this system has several disadvantages: recording times tend to be long as the speed of rotation of the drum is restricted; it takes a significant amount of time to wind and unwind the photosensitive material on and from the drum; the recording mechanism is complicated; the system itself is not only large in size but also complicated; and the number of sheets processed per unit time is small.
FIGS. 1 and 2 show an example of the conventional image recorder (see Japanese Patent Application (OPI) No. 279973/87). In this image recorder 10, a magazine 14 containing a heat development photosensitive material 16 as a color photosensitive material is mounted on a machine body 12. The heat development photosensitive material 16 inside the magazine 14 is drawn out and cut in predetermined lengths before being wound on the outer periphery of an exposure drum 20 (in the direction of an arrow A). An exposure head 22 having luminous elements of trichromatic point sources is installed opposite the outer periphery of the exposure drum 20. The exposure drum 20 is reversely turned after the exposure of one image plane. The heat development photosensitive material is then stripped therefrom with a scraper 24 and sent via a water coater 26 to a developing transfer unit 28. On the other hand, an image receiving material 32 contained in a tray 30 is sent to the developing transfer unit 28 and superposed on the heat development photosensitive material 16 before being heated by a heater in the developing transfer unit 28. The heat development photosensitive material 16 is thereby developed and the developed image is transferred to the image receiving material 32. After the completion of transfer, the heat development photosensitive material 16 is sent to a waste tray 32 via a peeler 36, whereas the image receiving material 32 is sent to a discharge tray 42 via a dryer 40.
As shown in FIG. 2, the exposure head 22 is turned (in the direction of the arrow A) at high speed and used to perform a main scanning operation while the heat development photosensitive material 16 is wound on the exposure drum 20. The exposure head 22 is provided with three primary luminous elements 44, which are employed to perform subscanning in the direction of an arrow B. The luminous elements 44 are positioned along a guide bar 46 disposed on an axis parallel to the exposure head 22. A pair of pulleys 48, 50 disposed on a parallel axis and a wire 52 wound on the pulleys are employed to move the exposure head 22 to perform the subscanning operation. One end of the wire is fastened to the exposure head 22 and its mid-portion is wound on the pulleys 4, 50, while the other end is fitted to the exposure head 22 via a tension providing member 54.
After being cut by a cutter 18 in predetermined lengths, the heat development photosensitive material 16 within the magazine 14 is wound on the outer periphery of the exposure drum 20. The exposure drum 20 is turned by a motor (not shown) in the direction A. Each time the pulley 48 is turned, the exposure head 22 performs a subscanning operation while moving in the direction B. The subscanning operation is such that exposure is effected by a luminous elements only when the pulley 48 is driven clockwise (C). When the exposure drum 20 is reversely turned, the exposed heat development photosensitive material 16 is stripped by the scraper 24 from the outer periphery of the exposure drum 20 and sent via the water coater 26 to the developing transfer unit 28.
The image receiving material 32 taken out of the tray 30 is sent to the developing transfer unit 28 and superposed on the heat development photosensitive material 16 so that the emulsion layers of both the materials adhere to each other. When the heater within the developing transfer unit 28 is operated, the image exposed to the heat development photosensitive material 16 is subjected to heat development, whereby the resulting image is transferred to the image receiving material 32. Image transfer is carried out with certainty because water is applied by the water coater 26 to the emulsion layer of the heat development photosensitive material 16. The heat development photosensitive material 16 from which the image has been transferred is discharged into the waste tray 38, whereas the image receiving material 32 is discharged via the dryer 40 into the discharge tray.
In the conventional image recorder thus constructed, the heat development photosensitive material 16 cut in lengths is wound on the exposure drum to record a color image, and the exposed color photosensitive material is sent to the processing unit for processing purposes. It takes a significant amount of time to wind and unwind the photosensitive material on and from the exposure drum 20. Moreover, since the main scanning and the subscanning with the three luminous elements 44 for effecting trichromatic exposure corresponding to the spectral sensitivity characteristics of the heat development photosensitive material 16 are employed to record an image on the heat development photosensitive material 16 of the exposure head 20, the total recording time is considerably long. Further, the recording size is disadvantageously limited to what corresponds to the diameter of the exposure drum 20.
A light-emitting diode can be uses as an image recording element for a scanning type color image recording system employing a silver salt photosensitive material (color paper, color image recording material for a heat developing transfer system, etc.). In order to match the spectral characteristics of the light-emitting diode and those of the photosensitive material, the following may be used:
R (red) light .fwdarw. C (cyan) color development PA0 G (green) light .fwdarw. M (magenta) color development PA0 B (blue) light .fwdarw. Y (yellow) color development or PA0 IR (infrared) light .fwdarw. C color development PA0 G light .fwdarw. M color development PA0 Y light .fwdarw. Y color development
In general, the luminous output of a B light-emitting diode is small, and hence the use of IR, G and Y light is advantageous when a scanned image is to be recorded. Recording using a scanning process, namely, a process employing a drum scanning system, can be readily implemented using light-emitting diodes. However, an exposure method using such a point source is disadvantageous in that recording time tends to be long as sequential scanning is essential.
To eliminate such shortcomings, it is possible to use a light source formed of an array of light-emitting diodes mounted on a plate-like recording support 1 as shown in FIG. 3.
A light-emitting diode is, as shown in FIG. 4, generally produced by growing an epitaxial layer 23 on a monocrystalline substrate 21 of GaAs or GaP and further forming a p-n junction by diffusing impurities in the epitaxial layer 23. In FIG. 4 there is shown a combination of an electrode 22, diffusion preventing films for the diffusion, and an emission area 25 for each recording picture element, the emission area being partitioned by the diffusion preventing film 24. For a light-emitting diode having a, e.g., IR and G light, output that is, producing an output at a wavelength of 60 nm or greater, GaAs crystal is normally used, whereas GaP crystal is generally employed to generate Y light with a wavelength of 600 nm or less. Although GaAs monocrystal is opaque and therefore not permeable to light of any color GaP monocrystal is transparent to Y color light.
Therefore, in the case of alight source formed with an arrays of light-emitting diodes having Y light-emitting parts, crosstalk occurs between the adjoining luminous areas due to the electrode 22 and the boundary layer as shown in FIG. 5. It thus poses a serious problem to use such a light source to scan an record a wide-gradation, high quality color image. D1 in FIG. 5 represents a dot emitting light on receiving a signal, whereas D2 represents a dot receiving no signal. Crosstalk allows light to leak from the dot D1 to the dot D2.